A radio frequency identification (RFID) system for exchanging information between a reader/writer and an RFID tag by non-contact communications is known. Each of the reader/writer and the RFID tag includes an antenna device for transmitting and receiving a radio signal. For example, for an HF-range RFID system that uses 13.56 MHz as the communication frequency, the antenna device of an RFID tag and the antenna device of a reader/writer are coupled to each other mainly through an induction field and transmit and receive predetermined information.
In recent years, some communication terminal apparatuses, such as cellular phones, have introduced an RFID system, and the communication terminal apparatuses have been used as a reader/writer and an RFID tag. As a technique for providing a communication terminal apparatus with the RFID function, as described in, for example, Patent Literature 1, a technique for incorporating an antenna module in the communication terminal apparatus is known. The antenna module is one in which a planar coil antenna is disposed on a planar substrate.
PTL 1: Japanese Unexamined Patent Application Publication No. 2004-364199